1. Field of the Invention
The invention relates to an ion energy analyzer and a method for making and using the ion energy analyzer and, more particularly, to an ion energy analyzer for measuring ion energy distribution (IED) in a plasma processing system.
2. Description of Related Art
Plasma, or more generally an electrical discharge, has found extensive use in a variety of industrial applications, including material processing. For example, during semiconductor processing, plasma is often utilized to assist etch processes by facilitating the anisotropic removal of material along fine lines or within vias (or contacts) patterned on a semiconductor substrate. Examples of such plasma assisted etching include reactive ion etching (RIE), which is in essence an ion activated chemical etching process.
During plasma processing, ion energy, and more specifically the ion energy distribution (IED), is a process parameter that strongly influences the outcome of the reactive process at the substrate. For example, when performing an etching process on a semiconductor device, ion energy affects etch selectivity, etch rate uniformity, sidewall profile, residue control, etc. Due to the significance of this process parameter, the measurement of ion energy at a specific location within a plasma processing system is important for characterizing the effectiveness of the plasma state for processing the substrate.
In general, the IED is measured in plasma by immersing a grid and an ion collector in a beam of ions. The electric potential of the grid is varied, and only the ions in the beam of ions having sufficient energy to overcome the potential barrier imposed by the grid will pass through the grid and strike the ion collector. By collecting and measuring the ion current as a function of the potential on the grid, an integrated form of the IED can be acquired. Differentiation of this integral leads to the IED.
Although the IED has been measured extensively in plasma processes for decades using a variety of ion energy analyzers, most conventional analyzers suffer from a multitude of problems including, but not limited to: (1) Conventional analyzers perturb the processing plasma to an extent that the measurement is no longer characteristic of the conditions prevailing when processing a substrate; (2) Conventional analyzers fail to operate at large electric potentials; and (3) Conventional analyzers exhibit substantive noise arising from secondary electron emission within the analyzer.
While many attempts have been made to cure these shortcomings, they still remain and the plasma processing community continues to explore novel, practical solutions to these and other problems.